Pyrazole metal complex for absorbing carbon dioxide, method for preparing pyrazole metal complex, and method for absorption of carbon dioxide

ABSTRACT

A pyrazole metal complex for absorption of carbon dioxide, a method for preparing the pyrazole metal complex, and a method for absorbing carbon dioxide are provided; wherein the product produced by reacting pyrazole metal complex and carbon dioxide may be transformed into several economically valuable compounds.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional of co-pending application Ser. No.17/550,382 filed on Dec. 14, 2021; and this application claims thebenefit of U.S. Provisional Application Ser. No. 63/173,723, filed onApr. 12, 2021, and the benefit of Taiwan Patent Application Serial No.110127682 filed on Jul. 28, 2021. The entirety contents of all of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pyrazole metal complex for absorbingcarbon dioxide, a method for preparing pyrazole metal complex, andmethod for absorption of carbon dioxide; particularly, to a pyrazolemetal complex for absorbing carbon dioxide in the air, a method forpreparing pyrazole metal complex, and method for absorption of carbondioxide in the air.

2. Description of Related Art

Since the industrial revolution, excessive use of petroleum fuels hascaused massive emission of carbon dioxide, which has severely affectedthe world by causing problems such as the greenhouse effect, seawateracidification, ecological imbalance, and melting icebergs. Accordingly,how to reduce the content of carbon dioxide in the atmosphere and reducecarbon dioxide emissions is an important global issue.

Most of the carbon dioxide capture techniques currently applied in theindustry are disadvantageous of oxide sensitive, water sensitive, highvolatility, and high demand for renewable energy. Or, the products yieldafter capturing carbon dioxide are not reusable for synthesizingeconomically valuable compounds, and can only be stored in the saltwaterlayer deep underground.

Accordingly, it is desirable to provide a novel carbon dioxide capturetechnique, which is not sensitive to oxygen or water and the productsyielded from capturing carbon dioxide can be converted into othereconomically valuable compounds. It is also desirable that the compoundused for capturing carbon dioxide can be recovered as the originalcompound and continues to be used to capture carbon dioxide. In thisway, the cost of storing the product yield by capturing carbon dioxidecan be reduced, and other economically valuable compounds can besynthesized, the compound used to capture carbon dioxide can be reused,and the demand for environmental protection can be met.

SUMMARY OF THE INVENTION

The present invention provides a pyrazole metal complex for absorbingcarbon dioxide, wherein the pyrazole metal complex has the structure:

Wherein each of R₁, R₂, and R₃ is independently selected from a groupconsisting of hydrogen, substituted or unsubstituted C₁-C₆ alkyl group,and substituted or unsubstituted aryl group; and M₁ ^(n+) is selectedfrom a group consisting of Na⁺, K⁺, [K-18-crown-6 ether]⁺, Mn²⁺, Fe²⁺,Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu²⁺, Cu⁺, and Zn²⁺.

In one embodiment, R₁ is selected from a group consisting of hydrogen,methyl group, and benzyl group; each of R₂ and R₃ is independentlyhydrogen.

In one embodiment, M₁ ^(n+) is selected from a group consisting of Na⁺,K⁺, and [K-18-crown-6 ether]⁺.

The present invention also provides a preparing method of theabovementioned pyrazole metal complex, which comprises: step (a):providing a pyrazole compound having the structure:

and step (b): reacting a metal hydride with the pyrazole compound offormula (I-1) to obtain the pyrazole metal complex.

In one embodiment, step (b) further comprises tetrahydrofuran as asolvent.

The present invention further provides a method for absorbing carbondioxide in the air, comprising: step (1): providing a pyrazole metalcomplex of formula (I):

wherein each of R₁, R₂, and R₃ is independently selected from a groupconsisting of hydrogen, substituted or unsubstituted C₁-C₆ alkyl group,and substituted or unsubstituted aryl group; and M₁ ^(n+) is selectedfrom a group consisting of Na⁺, K⁺, [K-18-crown-6 ether]⁺, Mn²⁺, Fe²⁺,Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu²⁺, Cu⁺, and Zn²⁺; and step (2): reacting thepyrazole metal complex with carbon dioxide for absorbing carbon dioxide,wherein a product obtained by reacting the pyrazole metal complex andcarbon dioxide is a pyrazole amide formate of formula (II):

In one embodiment, R₁ is selected from a group consisting of hydrogen,methyl group, and benzyl group; each of R₂ and R₃ is independentlyhydrogen.

In one embodiment, M₁ ^(n+) is selected from a group consisting of Na⁺,K⁺, and [K-18-crown-6 ether]⁺.

In one embodiment, the reaction of the pyrazole metal complex and carbondioxide is carried out under an inert gas environment in step (2).

The present invention further provides another method for absorbingcarbon dioxide, which comprises: step (i): providing a pyrazole metalcomplex of formula (I)

wherein each of R₁, R₂, and R₃ is independently selected from a groupconsisting of hydrogen, substituted or unsubstituted C₁-C₆ alkyl group,and substituted or unsubstituted aryl group; and M₁ ^(n+) is selectedfrom a group consisting of Na⁺, K⁺, [K-18-crown-6 ether]⁺, Mn²⁺, Fe²⁺,Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu²⁺, Cu⁺, and Zn²⁺; and step (ii): reacting thepyrazole metal complex with carbon dioxide for absorbing carbon dioxide,wherein a product obtained by reacting the pyrazole metal complex andcarbon dioxide is a pyrazole amide formate of formula (II):

and step (iii): providing a double nitroso iron complex of formula (III)for reacting with the pyrazole amide formate of formula (II) to obtain ametal complex having the structure of formula (IV):

In one embodiment, in step (i), R₁ is selected from a group consistingof hydrogen, methyl group, and benzyl group; each of R₂ and R₃ isindependently hydrogen.

In one embodiment, in step (i), M₁ ^(n+) is selected from a groupconsisting of Na⁺, K⁺, and [K-18-crown-6 ether]⁺.

In one embodiment in step (ii), the reaction of the pyrazole metalcomplex and carbon dioxide is carried out under an inert gasenvironment.

In one embodiment, the method further comprises a step (iv): providing acalcium trifluoromethanesulfonate (Ca(OTf)₂) for reacting with the metalcomplex of formula (IV) to obtain a calcium oxalate (CaC₂O₄).

In one embodiment, the method further comprises a step (v): providing abis(pinacolato)diboron ((PinB)₂) for reacting with the metal complex offormula (IV) to obtain a carbon monoxide.

In one embodiment, the method further comprises a step (vi): providing a9-Borabicyclo(3.3.1)nonane (9-BBN) for reacting with the metal complexof formula (IV) to obtain a formic acid.

In one embodiment, the method further comprises a step (vii): providinga triethyl boride for reacting with the metal complex of formula (IV) toobtain a propionate.

In one embodiment, the method further comprises a step (viii): providinga zinc trifluoromethanesulfonate for reacting with the metal complex offormula (IV) to obtain a carbon dioxide reduction product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ¹³C solid NMR spectrum of Na-pyr of one embodiment of thepresent invention;

FIG. 2 is a powder X-ray diffraction pattern of Na-pyr and simulatedspectrum of one embodiment of the present invention;

FIG. 3 is a ¹³C solid NMR spectrum of K-pyr of one embodiment of thepresent invention;

FIG. 4 is a powder X-ray diffraction pattern of K-pyr of one embodimentof the present invention;

FIG. 5 is a ¹³C solid NMR spectrum of 18-K-pyr of one embodiment of thepresent invention;

FIG. 6 is a powder X-ray diffraction pattern of 18-K-pyr and simulatedspectrum of one embodiment of the present invention;

FIG. 7 is an IR vibration spectrum of Na-pyr-CO₂ of one embodiment ofthe present invention;

FIG. 8 is a ¹³C solid NMR spectrum of Na-pyr-CO₂ of one embodiment ofthe present invention;

FIG. 9 is a powder X-ray diffraction pattern of Na-pyr-CO₂ of oneembodiment of the present invention;

FIG. 10 is an IR vibration spectrum of K-pyr-CO₂ of one embodiment ofthe present invention;

FIG. 11 is a ¹³C solid NMR spectrum of K-pyr-CO₂ of one embodiment ofthe present invention;

FIG. 12 is a powder X-ray diffraction pattern of K-pyr-CO₂ of oneembodiment of the present invention;

FIG. 13 is a schematic diagram of an air capture system of oneembodiment of the present invention;

FIG. 14 is a schematic diagram of the detection results of the aircapture system of one embodiment of the present invention;

FIG. 15 is a schematic diagram of the detection results of the aircapture system of one embodiment of the present invention;

FIG. 16 is a schematic diagram of the detection results of the aircapture system of one embodiment of the present invention;

FIG. 17 is a schematic diagram of the detection results of the aircapture system of one embodiment of the present invention;

FIG. 18 is a schematic diagram of the detection results of the aircapture system of one embodiment of the present invention;

FIG. 19 is an IR vibration spectrum of the product of one embodiment ofthe present invention;

FIG. 20 is a ¹³C solid NMR spectrum of the product of one embodiment ofthe present invention;

FIG. 21 is a GC chromatogram of the product of one embodiment of thepresent invention;

FIG. 22 shows a ¹H NMR spectrum and a ¹³C NMR spectrum of the product ofone embodiment of the present invention;

FIG. 23 is a ¹³C NMR spectrum of the product of one embodiment of thepresent invention;

FIG. 24 is an IR vibration spectrum of the product of one embodiment ofthe present invention; and

FIG. 25 is a ¹³C NMR spectrum of the product of one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereafter, examples will be provided to illustrate the embodiments ofthe present invention. The advantages and effects of the invention willbecome more apparent from the disclosure of the present invention. Othervarious aspects also may be practiced or applied in the invention, andvarious modifications and variations can be made without departing fromthe spirit of the invention based on various concepts and applications.

[Synthesis and Identification of the Pyrazole Metal Complex]

Firstly, reaction formula (a) is carried out by reacting sodium withpyrazole:

The product synthesized by the above reaction is identified as sodiumpyrazolate (Na-pyr) according to the chemical shift (108.58/144.28 ppm)of the ¹³C solid NMR spectrum (FIG. 1 ), and comparison between thepowder X-ray diffraction pattern of the product and simulated spectrum(FIG. 2 ).

Reaction formula (b) is carried out by reacting potassium hydride withpyrazole:

The product synthesized by the above reaction is identified as potassiumpyrazolate (K-pyr) according to the chemical shift (111.19/139.35 ppm)of the ¹³C solid NMR spectrum (FIG. 3 ), and the powder X-raydiffraction pattern of the product (FIG. 4 ) supports that the producthas an orderly arrangement.

Further, reaction formula (C) is carried out by reacting potassiumhydride and 18-crown-6 ether with pyrazole:

The product synthesized by the above reaction is identified as[K-18-crown-6-ether][pyr] (18-K-pyr) according to the chemical shift(70.92, 100.66, 136.190 ppm) of the ¹³C solid NMR spectrum (FIG. 5 ),and comparison between the powder X-ray diffraction pattern of theproduct and simulated spectrum (FIG. 6 )

[Reaction of Pyrazole Metal Complex with Carbon Dioxide]

Firstly, reaction formula (d) is carried out by reacting Na-pyr withcarbon dioxide:

The reaction product Na-Pyr-CO₂ is identified according to the IRvibration spectrum (1716 cm⁻¹) (FIG. 7 ) and the chemical shift (152.64,138.80, 132.43, and 106.5 ppm) of the ¹³C solid NMR spectrum (FIG. 8 ).Also, an orderly arrangement of the product is supported by the powderX-ray diffraction pattern (FIG. 9 ).

Reaction formula (e) is carried out by reacting K-pyr and carbondioxide:

The reaction product K-Pyr-CO₂ is identified according to the JRvibration spectrum (1690 cm-1) (FIG. 10 ) and the chemical shift(151.89, 140.02, 130.44, and 105.97 ppm) of the ¹³C solid NMR spectrum(FIG. 11 ). Also, an orderly arrangement of the product is supported bythe powder X-ray diffraction pattern (FIG. 12 ).

[Pyrazole Metal Complex for the Capture of Carbon Dioxide]

An air capture system 1000 illustrated in FIG. 13 is provided fortesting the carbon dioxide capture ability of the pyrazole metalcomplex. The air capture system 1000 mainly includes an air compressor1, a flow controller 2, a tubing 3, a sample column 4, a drying tube 5,a flow detector 6, and a gas chromatograph 7. The air output by the aircompressor 1 is controlled at a flow rate of 200 mL/min by the flowcontroller 2 and passes through the tubing 3 contained with water sothat the air is humidified. Next, the air passes through the samplecolumn 4 filled with different pyrazole metal complexes whilst thepyrazole metal complex in the sample column captures the carbon dioxidein the air. After carbon dioxide is captured from the air by differentpyrazole metal complexes and water is removed from the air by the dryingtube 5, the air flows into the gas chromatograph 7 for detection of theconcentration of carbon dioxide.

First, the above-mentioned air capture procedure is performed with thesample column 4 filled with Na-pyr. Dry air and humidified air areindependently provided and the detection results are shown in FIG. 14 .According to the results shown in FIG. 14 , Na-pyr can capture 80percent of the carbon dioxide for 20 minutes and capture 50 percent ofthe carbon dioxide for 160 minutes whilst the air is humidified.However, the ability to capture carbon of the pyrazole metal complexesin dry air dioxide is poor.

Next, the air capture procedure is performed with the sample column 4filled with Na-3-methylpyrazolate (Na-3-mpyr) with a methyl substituentat position 3. Humidified air is provided and the detection result isshown in FIG. 15 . According to the result shown in FIG. 15 , Na-3-mpyrhas the ability to capture carbon dioxide from the humidified air.

Furthermore, the air capture procedure is performed with the samplecolumn 4 filled with K-pyr. Dry air and humidified air are provided andthe detection result is shown in FIG. 16 . According to the result shownin FIG. 16 , K-pyr can capture 20 percent of the carbon dioxide for 60minutes from the humidified air; K-pyr also has the ability to capturecarbon dioxide in dry air.

Next, the air capture procedure is performed with the sample column 4filled with K-3-methylpyrazolate (K-3-mpyr) with a methyl substituent atposition 3. Humidified air is provided and the detection result is shownin FIG. 17 . According to the result shown in FIG. 17 , K-3-mpyr has theability to capture carbon dioxide from the humidified air.

Furthermore, the air capture procedure is performed with the samplecolumn 4 filled with 18-K-pyr. Dry air and humidified air are providedand the detection result is shown in FIG. 18 . According to the resultshown in FIG. 18 , 18-K-pyr can capture over 95 percent of the carbondioxide for 20 minutes from the humidified air and the dry air.

According to the test results, each of pyrazole metal complexesincluding Na-pyr, Na-3-mpyr, K-pyr, K-3-mpyr, and 18-K-pyr has theability to capture carbon dioxide in the air.

The product obtained after capturing carbon dioxide by the pyrazolemetal complex can be further combined with different chemical reagentsto reduce carbon dioxide into economically valuable products.

[Conversion of Carbon Dioxide to Calcium Oxalate]

The product of Na-3-mpyr or K-3-mpyr capturing carbon dioxide is shownin formula (II-1):

Next, reacting the product (II-1) with the double nitroso iron complexof formula (III) to obtain a metal complex of formula (IV-1):

Furthermore, reacting the metal complex 2CO₂ of formula (IV-1) with thecalcium trifluoromethanesulfonate (Ca(OTf)₂), the product ischaracterized by the IR absorption peak at 1657 cm⁻¹ (FIG. 19 ). Theabsorption peak of the product obtained by reacting 2-¹³CO₂ is shiftedto 1633 cm⁻¹ (FIG. 19 ). According to the IR vibration spectrum, theformation of the carbon dioxide reduction product is confirmed. Inaddition, the carbon dioxide reduction product is also confirmed by thechemical shift 161.99 ppm in the NMR spectrum (FIG. 20 ).

[Conversion of Carbon Dioxide to Carbon Monoxide]

Similarly, reacting the product (II-1) of Na-3-mpyr or K-3-mpyrcapturing carbon dioxide with the double nitroso iron complex of formula(III) to obtain a metal complex of formula (IV-1). Then, reacting themetal complex 2-CO₂ and bis(pinacolato)diboron, the air after thereaction is collected and is confirmed by the gas chromatograph that thereaction converts carbon dioxide into carbon monoxide (FIG. 21 ).

[Conversion of Carbon Dioxide to Formic Acid]

Similarly, the product collected by reacting the metal complex 2-CO₂represented by formula (IV-1) with 9-borabicyclo(3.3.1)nonane isdissolved in heavy water. It is confirmed that the reaction convertscarbon dioxide into formate by the chemical shift 8.42 ppm in ¹H NM Rspectrum and 171.62 ppm in ¹³C NMR spectrum (FIG. 22 ).

[Conversion of Carbon Dioxide to Propionate]

Similarly, reacting the product (II-1) of Na-3-mpyr or K-3-mpyrcapturing carbon dioxide with the double nitroso iron complex of formula(III) to obtain a metal complex of formula (IV-1).

The product of reacting the metal complex 2-¹³CO₂ with triethyl borideis dissolved in heavy water. It is confirmed that the reaction convertscarbon dioxide into propionate by the chemical shift 165.28 ppm in ¹³CNMR spectrum (FIG. 23 ).

[Capture and Purification of Carbon Dioxide]

The product obtained by reacting metal complex 2-CO₂ represent byformula (IV-1) with zinc trifluoromethanesulfonate is characterized bythe IR absorption peaks at 1250 cm⁻¹ and 1176 cm⁻¹ (FIG. 24 ). When2-¹³CO₂ is used, the IR absorption peaks shift to 1225 cm⁻¹ and 1154cm⁻¹ (FIG. 24 ). According to the IR vibration spectrum, the formationof the carbon dioxide reduction product is confirmed. Also, it isconfirmed that the reaction converts carbon dioxide into a carbondioxide reduction product by the chemical shift 66.4 ppm and 65.6 ppm in¹³C NMR spectrum (FIG. 25 ) when 2-¹³CO₂ is used.

[Reduction of the Pyrazole Metal Complex]

After the pyrazole metal complex captures carbon dioxide, reacts withthe double nitroso iron complex represented by formula (III), andfurther reacts with calcium triflate to form calcium oxalate, the sideproduct obtained can further react with protonatedpentamethyldiethylenetriamine (PMDTA) to form a pyrazole compound andthe double nitroso iron complex represented by formula (III), whereinthe pyrazole can further convert into the pyrazole metal complex of thepresent invention. That is, the pyrazole metal complex of the presentinvention and the double nitroso iron complex can be recovered after thecapture of CO₂ and forming calcium oxalate.

In summary, the pyrazole metal complex of the present invention iscapable of capturing carbon dioxide efficiently, the product yieldsafter capturing carbon dioxide can be converted to several economicallyvaluable compounds such as carbon monoxide, calcium oxalate, formate,and propionate, or can be converted to carbon dioxide reduction productthrough reactions. Also, the pyrazole metal complex and the doublenitroso iron complex required in the reaction can further be recoveredand reused, which meets the requirements of low cost and environmentalfriendly.

What is claimed is:
 1. A method for absorbing carbon dioxide,comprising: step (i): providing a pyrazole metal complex of formula (I)

wherein R₁ is selected from a group consisting of hydrogen, methylgroup, and benzyl group; each of R₂ and R₃ is independently hydrogen;and M₁ ^(n+) is selected from a group consisting of Na⁺, K⁺,[K-18-crown-6 ether]⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu²⁺, Cu⁺,and Zn²⁺; and step (ii): reacting the pyrazole metal complex with carbondioxide for absorbing carbon dioxide, wherein a product obtained byreacting the pyrazole metal complex and carbon dioxide is a pyrazoleamide formate of formula (II):

and step (iii): providing a double nitroso iron complex of formula (III)for reacting with the pyrazolamide formate of formula (II) to obtain ametal complex having structure of formula (IV):


2. The method of claim 1, wherein step (i), M₁ ^(n+) is selected from agroup consisting of Na⁺, K⁺, and [K-18-crown-6 ether]⁺.
 3. The method ofclaim 1, wherein step (ii), the reaction of the pyrazole metal complexand carbon dioxide is carried out under an inert gas environment.
 4. Themethod of claim 1, further comprising: step (iv): providing a calciumtrifluoromethanesulfonate (Ca(OTf)₂) for reacting with the metal complexof formula (IV) to obtain a calcium oxalate (CaC₂O₄).
 5. The method ofclaim 1, further comprising: step (v): providing abis(pinacolato)diboron ((PinB)₂) for reacting with the metal complex offormula (IV) to obtain a carbon monoxide.
 6. The method of claim 1,further comprising: step (vi): providing a 9-Borabicyclo(3.3.1)nonane(9-BBN) for reacting with the metal complex of formula (IV) to obtain aformic acid.
 7. The method of claim 1, further comprising: step (vii):providing a triethyl boride for reacting with the metal complex offormula (IV) to obtain a propionate.
 8. The method of claim 1, furthercomprising: step (viii): providing a zinc trifluoromethanesulfonate forreacting with the metal complex of formula (IV) to obtain a carbondioxide reduction product.